Some preliminary remarks on the origin 

 of isolated vascular bundles in herbaceous 

 dicotyledonous plants. 



By 



Henning E. Petersen. 



Of late years American botanists, Ch. Edw. Jeffrey and his 

 followers, have thoroughly treated the question oft he evolutionary 

 development of the stem-structure in herbaceous, dicotyledonous 

 plants. Starting from the undoubtedly correct hypothesis that 

 recent herbaceous plants are derived from trees and shrubs they 

 have formed a theory of the evolutionary phylogeny of the her- 

 baceous stem. They are agreed that an unbroken woody cylinder 

 is the primitive stage and that vascular bundles in the herbace- 

 ous stem are separate parts of this cylinder, but they are not 

 so agreed as to the details. For instance, some authors attach 

 much more importance to the medullary rays than others. At 

 first sight their views are very convincing ; gradually doubt arises ; 

 at last it becomes obvious that weighty objections can be made 

 against their views. One is surprised at the neglect of this sub- 

 ject as shown by the European literature dealing with it, that 

 is, with the exception of "the hypothesis of Sachs and de Bary", 

 which, as far as I can see, can hardly be attributed to these authors. 

 In the following I shall sum up the main points of their theories, 

 and setting up a counter-hypothesis I shall try to shake the 

 reliability of their theories. In their considerations they naturally 

 start from the oldest forms of vascular plants. 



These types are very thoroughly treated by Jeffrey in his 

 text-book "The anatomy of woody plants", in which work is re- 

 presented the conception which I now criticise. First he men- 



